The sandalwood oil from the East Indies used frequently in the perfume industry contains primarily the sesquiterpenes .alpha.-and .beta.-santalol (A and B respectively), which also produce the characteristic mild woody odor of the oil. ##STR3##
The limited availability and the high price of sandalwood oil motivated the development of chemical syntheses for A and B, which nevertheless could not be utilized industrially. The replacement products used currently are chiefly terpenylcyclohexanols (review article: I. S. Aulchenko and L. A. Kheifits, American Perfumer and Cosmetic, 37 (1970), which are obtained by an acid-catalyzed reaction of camphene with phenol derivatives and subsequent catalytic hydrogenation. Complex mixtures are thereby formed, which consist only to a small extent of active perfumes of the sandalwood type, and are frequently contaminated with terpenylphenols.
It would be natural to assume that the production of the most natural sandalwood scent possible would be expected from compounds which are structurally similar to the santalols A and B shown above, and which have a comparable molecular size or number of carbon atoms. However, this implies the synthesis of a comparatively complex ring system which, as shown above, requires complicated procedures and purification steps, or the introduction of comparatively long side chains with appropriate partial structure into a simpler skeletal structure. In the latter process, the results showed little success with respect to the shades of odor (review article: G. Ohloff, Fortschr. Chem. Forsch., Vol. 12/2, page 212, 1969). Thus, in U.S. Pat. No. 4,052,341, besides higher-molecular-weight compounds or those with longer chains, the compound 3-methyl-5-(2,2,3-trimethylcyclopent-3-ene-1-yl)pentane-2-ol, a compound in which a rather long side chain containing a secondary hydroxyl group is bonded to the simple trimethylcyclopentene ring skeleton, is also shown. The process specified for industrial preparation of this substance produces a mixture of isomers which contains a large fraction of 6-(trimethylcyclopent-3-ene-1-yl)hexane-3-ol, so that the odor intensity and quality of the products are somewhat less satisfactory. The patent mentioned states that longer chains with secondary hydroxyl groups must be introduced in order to obtain the desired notes or shades of odor.
German Offenlegungsschrift No. 1,922,391 describes campholenylidenealkanols, namely campholenylidenepropanol, 2-campholenylidenebutanol and campholenylideneisopropanol, which have shades of fragrance reminiscent of musk, sandalwood, or of the aroma of figs. The disadvantage of these compounds too is that, because of the unsaturation in their side chains, as is frequently the case with such unsaturated compounds, they are chemically less stable, they have a tendency toward aging reactions, and are therefore less well suited as perfumes.